Biophysical influences and Appendicularia abundance differentiate zooplankton and age-0 fish communities spanning subarctic and Arctic bioregions

In the Canadian Arctic and subarctic, zooplankton and age-0 fish are highly sensitive to environmental variation, but boom-and-bust recruitment makes their response to environmental changes difficult to predict. We combined hydroacoustic and continuous plankton recorder (CPR) surveys to assess the main biophysical drivers influencing the distribution of zooplankton and age-0 fish in the epipelagic waters across a vast latitudinal gradient ranging from the Gulf of St. Lawrence (49°N) to northern Baffin Bay (77°N). Multivariate analyses suggested 2 distinct near-surface (~7 m) zooplankton communities, one in the subarctic combined Labrador Shelf/Gulf of St. Lawrence region and another in the Arctic Baffin Bay region, with differences primarily explained by latitude, surface chlorophyll concentration, and the abundance of Appendicularia. Surface currents connect the surface zooplankton communities on the Labrador Shelf with those in the Gulf of St. Lawrence, and the communities in the relatively productive waters of northern Baffin Bay with those in western Baffin Bay. Epipelagic (0-100 m) zooplankton abundance was most influenced by surface chlorophyll concentration, salinity, and latitude. Meanwhile zooplankton abundance, time of day, sea surface temperature, and latitude all had significant effects on epipelagic age-0 fish abundance, including polar cod Boreogadus saida . We conclude that food availability and latitudinal gradients in environmental conditions drive epipelagic community abundance and distribution in Arctic and subarctic regions. Furthermore, we demonstrate that combining CPR and hydroacoustics can improve the taxonomic and the vertical and latitudinal resolutions of the distributions of zooplankton and age-0 fish communities when opportunistic sampling is conducted during transit.